From the Guidelines
Phentermine can cause menstrual irregularities in women, including menstrual spotting, due to its effects on the metabolism of estrogen and progestins. According to the study published in Obesity Reviews in 2023 1, phentermine, particularly when used in combination with topiramate, can alter the metabolism of estrogen and progestins, leading to menstrual spotting in women taking birth control pills. This suggests that phentermine may have a similar impact on menstrual cycles in general, potentially causing irregularities.
The exact mechanisms by which phentermine affects menstrual cycles are not fully understood but are thought to involve the drug's influence on the central nervous system and stress hormones, which can disrupt the hypothalamic-pituitary-ovarian axis regulating menstruation. Women taking phentermine may experience a range of menstrual changes, including missed periods, irregular bleeding, or changes in flow volume and duration.
It is essential for women experiencing significant menstrual changes while taking phentermine to discuss these with their healthcare provider 1. The provider may recommend continuing with careful monitoring, adjusting the dosage, or discontinuing the medication, depending on the severity of symptoms. Suddenly stopping phentermine without medical guidance is not advised, as this can cause withdrawal symptoms. Women with pre-existing menstrual disorders or hormonal conditions should be particularly cautious when considering phentermine treatment, as the potential for menstrual irregularities may be higher in these populations.
Key considerations for healthcare providers prescribing phentermine to women of childbearing age include:
- Monitoring for menstrual irregularities and other potential side effects
- Counseling patients on the potential risks and benefits of phentermine treatment
- Regularly reviewing the need for continued phentermine treatment, especially if menstrual irregularities or other side effects occur
- Considering alternative weight loss treatments for women with a history of menstrual disorders or hormonal conditions.
From the Research
Menstrual Irregularities and Phentermine
- There is limited research directly linking phentermine to menstrual irregularities 2, 3.
- A study on the long-term effects of weight-reducing drugs, including phentermine, found that it can reduce body weight and lower blood pressure, but did not specifically address menstrual irregularities 2.
- Another study on the safety and effectiveness of longer-term phentermine use found that patients using phentermine continuously for more than 12 months experienced more weight loss, but did not report any menstrual irregularities 3.
- Menstrual irregularities can be caused by various factors, including hormonal changes, weight changes, and certain medications 4.
- Hormonal contraceptives, which are not directly related to phentermine, can improve medical conditions associated with hormonal changes related to the menstrual cycle, such as acne, endometriosis, and premenstrual dysphoric disorder 5.
- Progestin-only contraceptives, which are also not directly related to phentermine, can cause endometrial break through bleeding, leading to discontinuation 6.